Pressure relief valves, utilizing a variable number of control weights to determine the relief pressure at which the valve is actuated, are employed commercially. However, for large size valves such design has a severe disadvantage, the amount of weight required. For example, a weighted relief valve with a 12" diameter would require a total of 1131 pounds of weight (movable cap plus control weights) for a relief pressure of only 10 psig. Such high total weights make these valves very expensive to manufacture, to support in their installation, and to maintain.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an improved pressure relief valve. Another object of the invention is to provide a light-weight pressure relief valve which is inexpensive to manufacture and install. A further object of the invention is to provide an improved pressure relief valve which can be readily maintained.
The present invention provides a light-weight pressure relief valve which avoids the foregoing difficulties of the weighted pressure relief valve. A relief valve in accordance with the present invention comprises a hollow valve body having one or more large vent ports in its side wall and a small pilot orifice in a first end wall. Fluid communication is provided between the interior of the valve body and the pressurized container to be protected against excessive pressure. A light-weight sleeve, closed at one end, telescopes over the first end of the valve body to close the vent ports under normal pressure conditions in the pressurized container. A pressure actuatable element is positioned on the outlet of the pilot orifice to permit fluid communication between the valve body interior and the interior chamber formed in the sleeve between the closed end of the sleeve and the first end of the valve body. The ratio of (a) the inside surface of the sleeve which is effectively perpendicular to the direction of movement of the sleeve and is exposed to fluid pressure in the interior chamber to (b) the area of the pilot orifice, and the ratio of (c) the weight of the sleeve to (d) the effective weight of the resistance of the pressure actuatable element are such that the pressure in the pressurized container necessary to move the pressure actuatable element to unblock the pilot orifice is substantially more than the pressure in the interior chamber necessary to move the sleeve to open the vent ports.